You can insert records into a fixed-length RRDS either sequentially or directly.

Sequential Insertion. Insertions into a fixed-length RRDS go into empty slots. When a record is inserted sequentially into a fixed-length RRDS it is assigned the next relative record number in sequence. If the slot is not empty, VSAM sets an error return code, indicating a duplicate record. The assigned number is returned in the argument field of the RPL.

Direct Insertion. Direct or skip-sequential insertion of a record into a fixed-length RRDS places the record as specified by the relative record number in the argument field of the RPL. You must insert the record into a slot that does not contain a record. If the slot specified does contain a record, VSAM sets an error return code in the RPL and rejects the request.

If the insertion is to the end of the control interval, the record is placed in a new control interval.